1. Field of the Invention
The present invention is directed to methods for stimulating the motility of the gastrointestinal system in a patient which comprises administering peptidyl analogs that possess agonistic ghrelin activity, a prodrug thereof, or a pharmaceutically acceptable salt of said analogs or said prodrug.
2. Description of the Related Art
Gastrointestinal (GI) motility is a coordinated neuromuscular process that transports nutrients through the digestive system (Scarpignato, C., Dig. Dis., (1997), 15:112), the impairment of which may result in a variety of ailments including gastroesophageal reflux disease (GERD), gastroparesis (e.g., diabetic and post-surgical), irritable bowel syndrome (IBS), constipation (e.g. that associated with the hypomotility phase of IBS), emesis (e.g., that caused by cancer chemotherapy agents), ileus and colonic pseudo-obstruction (U.S. Pat. No. 6,548,501; U.S. Patent Application No. 20040266989). These various complications of interrupted GI motility contribute significantly to the health care burdens of industrialized nations (U.S. Pat. No. 6,548,501; Feighner, S. D. et al., Science, (1999), 284:2184-8).
“Ileus” refers to the obstruction of the bowel or gut, especially the colon (see, e.g., Dorland's Illustrated Medical Dictionary, p. 816, 27th ed. (W.B. Saunders Company, Philadelphia 1988)). Generally, any trauma to the bowel resulting in the release of inflammatory mediators leading to activation of inhibitory neural reflexes will result in the onset of ileus. Ileus may be diagnosed by the disruption of the normal coordinated movements of the gut, resulting in failure of the propulsion of intestinal contents (Resnick, J., Am. J. of Gastroentero., (1997), 92:751; Resnick, J., Am. J. of Gastroentero., (1997), 92:934). Ileus should be distinguished from constipation, which refers to infrequent or difficulty in evacuating the feces (see, e.g., Dorland's Illustrated Medical Dictionary, p. 375, 27th ed. (W.B. Saunders Company, Philadelphia 1988)).
Ileus may be brought about by a variety of causes such as parturition; intestinal ischaemia; retroperitoneal haematoma; intraabdominal sepsis; intraperitoneal inflammation, e.g., acute appendicitis, choecystitis, pancreatitis; fractures of the spine; ureteric colic; thoracic lesions; basal pneumonia; rib fractures; myocardial infarction; and metabolic disturbances. Post-partum ileus is a common problem for women in the period following childbirth and is thought to be caused by fluctuations in natural opioid levels as a result of birthing stress. Patients having undergone procedures such as major abdominal surgery including laparotomy for abdominal abscess or small intestinal transplantation (SIT×), chest, pelvic or orthopedic surgery, often suffer from a period of transient impairment of bowel function called post-surgical or post-operative ileus (referred to hereinafter as POI).
POI commonly occurs for 24 to 72 hours following surgery. In some instances, the bowel dysfunction may become quite severe, lasting for more than a week and affecting more than one portion of the GI tract (Livingston, E. H. et al., Digest. Dis. and Sci., (1990), 35:121). Gastrointestinal dysmotility associated with POI is generally most severe in the colon. POI is characterized by abdominal nausea, distension, vomiting, obstipation, inability to eat and cramps. POI not only delays the normal resumption of food intake after surgery and prolongs hospitalization, but also fosters postoperative complications, especially aspiration pneumonia.
The administration of opioid analgesics to a patient after surgery may often contribute to and/or exacerbate existing bowel dysfunction, thereby delaying recovery of normal bowel function. Since virtually all patients receive opioid analgesics, such as morphine or other narcotics for pain relief after surgery, particularly major surgery, current post-surgical pain treatment may actually slow recovery of normal bowel function, resulting in a delay in hospital discharge and increasing the cost of medical care.
Agents which act to affect gastrointestinal motility may also confer beneficial effects upon patients suffering from emesis. Emesis, or vomiting, is often preceded by retching and may be accompanied by dry heaves. Emesis may be caused by imbalances in the digestive tract, such as ileus, dyspepsia, or inflammation of the gastric wall, or by imbalances in the sensory system or brain, such as motion sickness, migraine or tumors. Emesis may be self-induced such as in anorexia or bulimia, and it may also occur in response to severe pain, emotional responses (e.g., to disagreeable sights or odors), or pregnancy. Emesis is a common complication following the administration of many medications, particularly anti-cancer treatments such as chemotherapy. Prolonged episodes or repetitive emesis may result in a variety of injuries to the organism, including dehydration and electrolyte imbalances (Quigley, E. M. et al., Gastroentero., (2001), 120:263-86).
Agents which act to affect gastrointestinal motility may also confer beneficial effects upon patients suffering from gastroparesis. Gastroparesis, also called delayed gastric emptying, is a disorder in which the nerves to the stomach are damaged or stop working and the stomach takes too long to empty its contents. For example, following damage to the vagus nerve, the nerve which controls the movement of food through the digestive tract, the muscles of the stomach and intestines do not work normally and the movement of food is slowed or stopped. High blood glucose causes chemical changes in nerves and damages the blood vessels that carry oxygen and nutrients to the nerves. If blood glucose levels remain high over a long period of time, as is often the case in diabetes, the vagus nerve can be damaged; gastroparesis often occurs in people with type 1 diabetes or type 2 diabetes (Murray, C. D. et al., Gut, (2005), 54:1693-8).
The traditional therapies for impaired GI motility, such as that of ileus, gastroparesis and emesis, are considered ineffective. Current therapies for treating ileus include functional stimulation of the intestinal tract, stool softeners, laxatives such as Dulcolax®, lubricants, intravenous hydration, nasogastric suction, prokinetic agents, early enteral feeding, and nasogastric decompression. Nasogastric intubation to decompress the stomach has also traditionally been used to treat ileus.
Traditional pharmaceuticals used to treat impaired GI motility, such as that of ileus, include drugs that act to increase colonic motility, such as Leu13-motilin and prostaglandin F2 alpha, and prokinetic agents, such as Cisapride®. PROPULSID®, which contains Cisapride® monohydrate, is an oral gastrointestinal agent (U.S. Pat. No. 4,962,115) indicated for the symptomatic treatment of adult patients with nocturnal heartburn due to gastroesophageal reflux disease. Other prokinetic agents include, for example, metoclopramide, domperidone, ondansetron, tropisetron, mosap ride and itopride. Other treatments include administering adenosine-antagonizing pyrazolopyridine compounds (U.S. Pat. No. 6,214,843); pituitary adenylate cyclase activating peptide (PACAP) receptor antagonist in combination with a vasoactive intestinal peptide (VIP) receptor antagonist (U.S. Pat. No. 6,911,430); fedotozine (U.S. Pat. No. 5,362,756); neuropeptides (U.S. Pat. No. 5,929,035); and proteinase-activated receptor-2 antagonists (U.S. Pat. No. 5,929,035). In extreme cases, ileus has been treated with surgical intervention to unblock the colon.
These therapeutic regimens, however, suffer from numerous problems. For instance, PROPULSID® was recently removed from the market due to its potential to induce cardiac arrhythmias (U.S. Pat. No. 6,548,501). Adolor Corporation is presently in phase III clinical trials for a therapy to treat postoperative ileus using Alvimopan (Entereg®). Adolor's therapy, however, utilizes opioid receptor antagonists which merely block the side effects of opiate analgesics, rather than actually relieving the ileus condition. The phase III trials demonstrate marginal efficacy and minimal applicability for the treatment of ileus, particularly postoperative ileus.
Furthermore, these prior art methods for treatment of impaired GI motility lack specificity for different types of impairments, e.g., postoperative ileus or post-partum ileus. Also, these prior art methods offer no means for the prevention of impaired GI motility, such as that of ileus, gastroparesis and emesis. If impaired GI motility, such as that of ileus, gastroparesis and emesis, could be prevented or more effectively treated, hospital stays, recovery times, and medical costs would be significantly decreased with the additional benefit of minimizing patient discomfort.
Drugs which selectively target gut motility to correct gastrointestinal dysfunction caused by postoperative ileus would be ideal candidates for preventing and/or treating post-surgical and post-partum ileus. Such drugs would also be excellent candidates for the treatment of gastroparesis and/or emesis, particularly emesis associated with chemotherapies or other drug induced gastrointestinal dysfunction. Of those, drugs that do not interfere with the effects of opioid analgesics would be of special benefit in that they may be administered simultaneously with drugs for pain management with limited side effects.
Peptides affecting the release of growth hormone (GH) are now thought to exhibit gastrokinetic or “prokinetic” effects (U.S. Pat. No. 6,548,501; Peeters, T. L., J. Physiol. Pharmacol., (2003), 54 (supp 4):95-103 and references therein; Trudel, L. et al, J. Physiol. Gastrointest. Liver Physiol., (2002), 282:G948-52). Such growth hormone-releasing peptides, or GHRPs, are also referred to as growth hormone secretagogues (GHS). Exemplary growth hormone-releasing peptides (GHRPs) believed to exhibit prokinetic effects include GHRP-1, GHRP-2 and ghrelin.
Ghrelin, a recently discovered orexigenic hormone, is produced as a preprohormone that is proteolytically processed to yield a peptide of the following sequence: H-Gly-Ser-Ser-Phe-Leu-Ser-Pro-Glu-His-Gln-Arg-Val-Gln-Gln-Arg-Lys-Glu-Ser-Lys-Lys-Pro-Pro-Ala-Lys-Leu-Gln-Pro-Arg-NH2 (Kojima, M. et al., Nature, (1999), 402(6762):656-60; (SEQ ID NO; 338)). Ghrelin is produced by epithelial cells lining the fundus of the stomach and functions to stimulate appetite; its levels increase prior to a meal and decrease thereafter.
Ghrelin powerfully stimulates GH secretion from the anterior pituitary gland, mainly at the hypothalamic level, through its interaction with growth hormone secretagoue receptor (GHS-R) both in animals and in humans (Ukkola, O. et al., 2002 Ann. Med., (2002), 34:102-8; (Kojima, M. et al., Nature, (1999), 402(6762):656-60).
The native structures of ghrelin from several mammalian and non-mammalian species are known (Kaiya, H. et al., J. of Biol. Chem., (2001), 276:40441-8 and International Patent Application PCT/JP00/04907 [WO 01/07475]). A core region present in ghrelin is responsible for observed activity at the GHS receptor. The core region comprises the four N-terminal amino acids wherein the serine in the third position is normally modified with n-octanoic acid. In addition to acylation by n-octanoic acid, native ghrelin may also be acylated with n-decanoic acid (Kaiya, H. et al., J. of Biol. Chem., (2001), 276:40441-8).
Prior to the discovery that ghrelin is a native ligand for the GHS receptor, it was known that GHRPs controlled the release of growth hormone from the pituitary somatotrops. The hexapeptide His-D-Trp-Ala-Trp-D-Phe-Lys-amide (GHRP-6; (SEQ ID NO:342)), was found to release growth hormone from the somatotrops in a dose-dependent manner in several species including man (Bowers, C. Y. et al., Endocrinology, (1984), 114(5):1537-45). Subsequent chemical studies on GHRP-6 led to the identification of other potent, synthetic GHSs such as GHRP-I, GHRP-2 and hexarelin (Cheng, K. et al., Endocrinology, (1989), 124(6):2791-8; Bowers, C. Y., Novel GH-Releasing Peptides, Molecular and Clinical Advances in Pituitary Disorders, Ed: Melmed, S., Endocrine Research and Education, Inc., Los Angeles, Calif., USA, (1993), 153-7; and Deghenghi, R. et al., Life Sci., (1994), 54(18):1321-8). The structures of these compounds are as shown:
GHRP-IAla-His-D-(2′)-Nal-Ala-Trp-D-Phe-Lys-NH2;(SEQ ID NO: 339) GHRP-2D-Ala-D-(2′)-Nal-Ala-Trp-D-Nal-Lys-NH2;and (SEQ ID NO: 340) HexarelinHis-D-2-MeTrp-Ala-Trp-D-Phe-Lys-NH2.(SEQ ID NO: 341)GHRP-I, GHRP-2, GHRP-6, and hexarelin are classified as synthetic GHSs.
A number of recent studies have demonstrated the potential use of GHSs such as ghrelin, GHRP-6 and others to stimulate motor activity in the intestinal tract and to treat conditions such as ileus and emesis. For example, ghrelin and GHRP-6 have been shown to accelerate gastric emptying in rats and mice (Peeters, T. L., J. Physiol. Pharmacol., (2003), 54 (supp 4):95-103). In rats, ghrelin has been shown to reverse the delay of gastric emptying in a post-operative ileus model (Peeters, T. L., J. Physiol. Pharmacol., (2003), 54 (supp 4):95-103; Trudel, L. et al., J. Physiol. Gastrointest. Liver Physiol., (2002), 282(6):G948-52) and in laparectomized dogs, ghrelin was shown to improve POI in the treated animals (Trudel, L. et al, Peptides, (2003), 24:531-4). In septic mice, ghrelin and GHRP-6 accelerated gastric emptying although had little effect upon increasing transit in the small intestine (De Winter, B. Y. et al., Neurogastroenterol. Motil., (2004), 16:439-46).
In experiments designed to mimic hospitalization conditions for a human patient experiencing POI, laparectomized rats were exposed to opiates as well as ghrelin analog RC-1139 (Poitras, P. et al., Peptides, (2005), 26:1598-601). In an assay measuring gastric empyting, RC-1139 was shown to reverse POI in the control and laparectomized rats in the presence of morphine. It is thus believed that ghrelin exhibits gastrokinetic effects without interfering with opiate activity.
Ferrets exposed to the cytotoxic anti-cancer agent cisplatin exhibited significantly reduced occurrences of retching and vomiting following intracerebroventricular administration of ghrelin (Rudd, J. A. et al., Neurosci. Lett., (2006), 392:79-83) thus confirming the ability of ghrelin to reduce emesis in a manner consistent with its role in modulating gastro-intestinal functions. It is thought that ghrelin's role in modulating gastric motility is independent of the GH-secretory activation and may be mediated by the vagal-cholinergic muscarinic pathway (U.S. Patent Application No. 20060025566).
Ghrelin has also been shown to increase gastric emptying in patients with diabetic gastroparesis (Murray, C. D. et al., Gut, (2005), 54:1693-8).
It is interesting to note that in the studies referenced above, the ghrelin or ghrelin analog was administered using intraperitoneal (ip), intravenous (iv) or intracerebroventricular (icv) injection. Other disclosures (U.S. Pat. No. 6,548,501; U.S. Patent Application No. 20020042419; U.S. Patent Application No. 20050187237; U.S. Patent Application No. 20060025566) report on the oral administration of GHSs as a means to treat impaired gastrointestinal motility.
Very few compounds are known in the art to be useful for treating impaired GI motility and more compounds affecting gastrointestinal motility, e.g. stimulation of motility, would be highly desirable. Compounds affecting gastrointestinal kinetics are useful in the treatment of interruptions in normal GI functions such as ileus and emesis.